Adhesion enhancement of chromium tanned heavy-duty leather (Salz leather) under extreme conditions using photoreagents as surface primers

The work described investigates the development of photoreagents as surface primers for the enhancement of adhesion with heavy-duty leather surfaces (Salz). Several reagents were investigated which included 4-azidophenol (1), 3-azidophenol (2), 4-(2,2′-iminodiethanol)-3-nitrophenylazide (4) and 4-azido-(2,2′-iminodiethanol)benzamide (6) and used as an intimate mixture with commercial polyurethane adhesive (Solibond PU39) to enhance the adhesion of Salz leather surfaces. The photoreagents upon UV irradiation covalently attach to the leather surface enriching it with new functionalities to provide sites for bonding with the adhesive layer. The adhesion strength of photo primer treated leather samples were tested using the T-peel test against abraded leather surfaces under dry and wet conditions. Compounds 4 and 6 on T-peel testing were found to enhance adhesion strength by 99% under dry conditions and 163% and 157%, respectively, under wet conditions. The observed failure type was cohesive within the substrate when photoreagents were used, suggesting covalent bonds formation at the interface in addition to the usual van der Waals forces and hydrogen bonds affecting adhesion.